There are many things I would change about the way Perl installs on Win32. Whether the AS version or the standard distribution. The major change I would make is that I would do away with the <lib>\auto\... directories and place all dlls generated by building XS modules into the perl\bin. In this way, when a new perl is installed, it would empty perl\bin before installing thereby forcing all XS modules to have to be re-built before use.

There are also a bunch of other reasons why having all the XS-built dlls in a single place makes sense for purely Win32 reasons.

Distinguishing <install>\site\lib by version, is the wrong way to go. 99% of what lives in Perls lib directories is Pure Perl and so unaffected by version changes. It simply isn't necessary to replace or duplicate the vast majority of it when the binaries change.

The real problem is the mixing of the non Perl source parts (DLLs/SOs) with the Perl sources in the same subtree. And that's a big flaw (one of several) in the overall architecture of the Perl distributions. AS simply try to work with it as far as possible.